Stacks
What does 'stacks' mean?
Windows, Windows 6
Question marked as
Stacks is a way of keeping the clutter on your Mac desktop to a minimum.
If you keep lots of misc files and docs on the desktop, the feature will "stack" like documents into little piles rather than allow them just to lie about all over the desktop and add to chaos. PDF files will be ordered into a stack, images will be ordered into a stack, there will be a stack of documents and a stack for screenshots will appear. To view the files that are in a stack, you simply click the stack and the files spread out onto the desktop. Click again and the file return to their little stack.
I've taken advantage of the feature for some time now and find it helpful.
Use desktop stacks on Mac - Apple Support